Catalytic cracking method for treating a fraction having a low amount of Conradson carbon

ABSTRACT

The present invention discloses a process for the catalytic cracking of a weakly coking feedstock having a Conradson carbon residue of 0.1% by weight and a hydrogen content of greater than 12.7% by weight, comprising at least a feedstock cracking zone, a zone for separating/stripping the effluents from the coked catalyst particles and a zone for regenerating said particles, characterized in that at least a solid carbon material in the fluidized state, having a carbon content equal to or greater than 80% by weight, is injected upstream of and/or during the catalyst regeneration step into a dense bed of coked catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT/FR2012/051505, filed on Jun.29, 2012, which claims priority from FR 1155852, filed on Jun. 30, 2011,and U.S. Provisional Application No. 61/521,101, filed on Aug. 8, 2011.

The field of the present invention is that of the catalytic cracking ofpetroleum fractions, more particularly fractions which have a lowConradson carbon residue and a high hydrogen content and which,consequently, make it difficult to obtain the heat balance of the FCC(fluid catalytic cracking) unit.

In an FCC unit, the heat balance is mainly provided by the combustion ofcoke deposited on the catalyst during the cracking step. The heat ofcombustion allows the catalyst to be heated to temperatures typicallyranging from 670 to 750° C. The catalyst releases the heat stored in theregenerator into the reactor to vaporise the feedstock to be cracked,which is injected in liquid form, and to provide the energy necessaryfor cracking the feedstock via overall endothermic reactions. An FCCunit is said to be a thermally balanced unit since the energy producedin the regenerator is therefore transported to and then consumed in thereactor by circulation of the catalyst. Typically, the catalyst entersthe regeneration zone with a coke content (defined as the ratio of themass of coke to the mass of catalyst expressed as a percentage byweight) of between 0.5 and 1.45% by weight and leaves said zone with acoke content of between 0.1 and 0.5% by weight for regeneratorsoperating in partial combustion mode or between 0.1 and 0.05% by weight,or even less than 0.01% by weight, for regenerators operating incomplete combustion mode. When a regenerator is operating in partialcombustion mode or in complete combustion mode, the combustion isperformed with a gas containing oxygen.

In complete-combustion regeneration, all of the coke is burnt (typicalCO (carbon monoxide) content in the flue gas close to zero) whereas inpartial combustion mode the combustion of the coke produces CO with acontent of a few percent by volume, typically 0.5 to 10% by volume,depending on the air throughput and the degree of completeness of thecombustion in the case of incomplete combustion.

The Conradson carbon residue (or CCR) of the feedstock is defined by theASTM D 482 standard and represents, for those skilled in the art, ameasure of the amount of coke that the feedstock may produce during thecatalytic cracking reaction that takes place in the main reactor of theunit. Depending on the Conradson carbon residue of the feedstock, it ispossible to size the unit for a coke yield corresponding to the crackingof the feedstock so as to meet the heat balance of the unit that willcontrol the correct operation thereof.

Conventional heavy fractions treated in an FCC unit generally haveConradson carbon values lying in the range from 0.2 to 10% by weight.

The fractions treated in an FCC unit according to the present inventionmay have a Conradson carbon residue equal to or less than 0.1% by weightand a hydrogen content equal to or greater than 12.7% by weight.

EXAMINATION OF THE PRIOR ART

To equilibrate the heat balance, those skilled in the art know to pushthe combustion in the regenerator by injecting thereinto more air for agiven amount of coke, i.e. to reduce the volume percentage of carbonmonoxide (CO) in the flue gas, which contributes to increasing thetemperature in the said regenerator and necessarily helps to meet theheat balance of the unit.

When this situation is not sufficient or possible, it is known in theprior art to recycle into the regenerator a fuel in liquid form in aburner generally placed in the dense phase of the catalyst bed. Thisfuel, often called by those skilled in the art “high-viscosity fuel” or“torch oil”, generally contains one or more predominantly aromatic“heavy” fractions having an initial boiling point above 360° C. Thesefractions may come from the FCC unit or any other conversion unit in therefinery, such as a coker, a visbreaker, etc. It is also possible to useother types of fuel, such as fuel oil No. 2 or else fuel oils notmeeting the specifications required for commercializing them. Thisinjection of fuel into the regenerator is a common practice in thestart-up phases of the unit, but may be a source of problems when usedcontinually. This is because, since the temperatures in the regeneratorare around 650° C. to 750° C., a portion of the recycle vaporizes,forming cracked gases that are not entirely oxidised in the dense phaseof the regenerator and will therefore be found in the dilute phase ofthe regenerator where they thus run the risk of creating hot spots thatmay be damaging to the proper operation of the regenerator. Thisphenomenon, often called “afterburning” or “post-combustion”, may bedefined as further combustion at an undesired point in the regenerator,for example in the dilute phase where the solid catalyst is present in asmaller amount, or at the inlet of or inside one of the cyclones alsopresent in the enclosure of the regenerator, or else in the combustiongas discharge lines. This term “afterburning”, well accepted andpracticed by those skilled in the art, will be used in the rest of thetext.

Moreover, this recycle stream runs the risk of burning in the catalystbed, locally forming a high-temperature flame front. This flame frontgenerates hot spots with locally high temperatures within the catalystbed. Since steam also forms when these hydrocarbons are burnt, suchlocal high temperatures combined with the presence of steam weaken theactive part of the catalyst (zeolite) and thus deactivate its crackingfunction. It is referred to as hydrothermal catalyst deactivation. Thus,the lighter the recycle fraction, the richer it is in hydrogen and themore it generates steam by combustion in the regenerator. All theseundesirable phenomena described above are obviously exacerbated as theamount of liquid fuel recycled into the regenerator, to maintain theheat balance of the FCC unit, increases.

In such a context, that is to say with a feedstock that produces littlecoke during the cracking operation, and to avoid continuously injectingliquid hydrocarbons (or torch oil), which are responsible inter alia forthe afterburning and degradation of the catalyst, into the regenerator,refiners have often chosen to install a feedstock preheat furnaceupstream of the cracking reactor using a fuel having a high hydrogencontent. Adding such a preheat furnace therefore makes it possible tosupply the heat, which will be added to that produced by the combustionof the coke, to the catalyst in the regenerator and thus equilibratesthe heat balance of the unit. The supply of heat by the preheat furnacewill be greater the lesser the amount of heat supplied by theregenerator. However, there is a maximum preheat temperature limit forthe feedstock, which corresponds to the cracking onset temperaturethereof. It should be pointed out that installing such preheat furnacesis expensive, not only in terms of purchase cost but also operating costbecause of the external energy consumed.

In one of its first objectives, the present invention aims to provide aprocess for the catalytic cracking of a weakly coking feedstock, havinga Conradson carbon residue equal to or less than 0.1% by weight and/or ahydrogen content equal to or greater than 12.7% by weight, whichcomprises the injection in divided state, into the dense fluidized bedof the regenerator, consisting of relatively coked catalyst particles,of a coke-rich material making it possible to increase the amount ofcoke to be burnt off in the regenerator without promoting the formationof hot spots (afterburning) around the catalyst particles so as toprevent them from being deactivated.

It is known to inject coke-type compounds into cracking reactors and toblend them with the regenerated catalyst in one or more stages, theobjective being to promote demetallization of heavy feedstocks, heavymetals of the nickel and vanadium type being trapped in the pores ofsaid coke. Such applications are claimed in U.S. Pat. Nos. 3,092,568 and4,875,994.

In U.S. Pat. No. 4,828,680, coke in powder form, dispersed in freshcatalyst, is injected into the regenerator as catalyst make-up, the cokeparticles having a size comparable to that of the fresh crackingcatalyst. The problem encountered in this type of coke injection is thatof how to disperse the catalyst into the coke mixture homogeneouslybefore it is injected into the regenerator.

A second objective of the invention is to ensure that the dispersion ofthe coke within the coked catalyst particles or on the catalystparticles undergoing regeneration is homogeneous.

BRIEF DESCRIPTION OF THE INVENTION

The present invention applies both to FCC units using a reactoroperating in upflow mode (called a “riser” reactor) and to units using areactor operating in downflow mode (called a “downer” reactor).

The present invention also applies to FCC units operating with a singlereactor (in upflow mode or downflow mode) and to FCC units operatingwith two or more reactors. In general, when the FCC units operate withtwo reactors—a main reactor and a secondary reactor—they operate inmaximum gasoline or maximum GPL mode, or else in maximum distillate orLCO (light cycle oil) mode, these reactors are riser reactors, but aunit operating with two downer reactors or with one riser reactor andone downer reactor would not be outside the scope of the presentinvention.

For this purpose, the invention relates to a process for the catalyticcracking of a weakly coking feedstock having a Conradson carbon residueequal to or less than 0.1% by weight and a hydrogen content equal to orgreater than 12.7% by weight, said process being implemented in a unitcomprising at least a feedstock cracking zone, a zone forseparating/stripping the effluents from the coked catalyst particles anda zone for regenerating said particles, characterized in that at least asolid carbon material in the fluidized state, having a Conradson carbonresidue equal to or greater than 10% by weight, is injected upstream ofand/or during the catalyst regeneration step into a dense bed of cokedcatalyst in the regeneration zone.

According to the invention, the process is such that:

-   -   (a) at least one solid carbon material in the fluidised state,        having a carbon content equal to or greater than 80% by weight,        is dispersed on the coked catalyst particles:        -   (i) upstream of the regenerating zone and downstream of the            separating/stripping zone, and/or        -   (ii) in the zone for regenerating catalyst within the coked            catalyst particles of a dense bed.    -   (b) the amount of solid carbon material in the fluidized state        dispersed within the coked catalyst particles of the dense bed        is adjusted so as to deliver an additional amount of coke Q_(C)        to the catalyst so as to satisfy the following equation (I):        Q _(c) =Q _(t) −Q _(i)  (I),        in which Q_(i) is the initial coke content of the coked catalyst        after the feedstock has been cracked and a or delta coke is the        coke content necessary for maintaining the temperature of the        regenerated catalyst and therefore the heat balance of the        process,    -   (c) the mixture of coked catalyst particles and solid carbon        material is burnt in the regeneration zone to produce a        regenerated catalyst having a reduced content of carbon        material,    -   (d) the regenerated catalyst is mixed with the weakly coking        feedstock in the cracking zone to produce the coked catalyst        particles and the effluents,    -   (e) the coked catalyst particles are separated from the        effluents in the separating/stripping zone, then the coked        catalyst particles are sent back to the regeneration zone.

Advantageously, all of the added carbon material may be burnt within theregeneration zone. Indeed, if the added carbon material were notcompletely burnt, it would result in formation of coke dust which wouldbe partly recovered in the cyclones of the disengager of theseparating/stripping zone and partly recovered in the cyclones of theregeneration zone, where this coke dust is responsible of afterburningand accelerated degradation of the cyclones.

In the present application, the terms upstream and downstream arerelative to the envisaged circulation of the catalyst in theregenerating zone.

The carbon material may be fluidized, by any means, in a liquid orgaseous effluent not amalgamating with the carbone material, preferablyair.

According to the invention, the amount of solid carbon material in thefluidized state dispersed within the coked catalyst particles of thedense bed is adjusted so as to deliver an additional amount of cokeQ_(C) to the catalyst so as to satisfy the following equation (I):Q _(c) =Q _(t) −Q _(i)  (I),in which Q_(i) is the initial coke content of the coked catalyst afterthe feedstock has been cracked and Q_(t) or delta coke is the cokecontent necessary for maintaining the temperature of the regeneratedcatalyst and therefore the heat balance of the process.

In particular, Q_(t) may be chosen to be from 0.5 to 1% by weight whenthe regeneration zone comprises only a single step and from 0.8 to 1.45%by weight for a partial combustion in the first stage of a regenerationzone of a multistage regenerator having at least two regeneration steps.

The carbon material may be chosen from the following: coke resultingfrom the coking of coal; coke from cokers for hydrocarbon effluentshaving a boiling point above 350° C. chosen from heavy effluentfractions coming from the main cracking reaction, HCOs (heavy cycleoils) with a distillation range typically between 360 and 440° C. andslurries with a distillation range above 360° C. (denoted by 360°+);biomass residues coming from the conversion of wood and/or cellulose;powdered coal dissolved in a fluid hydrocarbon and/or injected byblowing or spraying; asphalt-rich fractions coming from deasphaltingunits; non-utilizable waxes coming from the liquefaction of coal by anindirect (GTL) process or from a Fischer-Tropsch process for convertinggas into hydrocarbons; and a mixture of said fractions.

The feedstock injected into the cracking zone may be chosen from thegroup comprising the following: purges or bleeds from a hydrocrackingunit; feedstocks based on vacuum-distilled gas-oil fractions having aboiling point above 350° C. and having hydrogen contents equal to orgreater than 12.7% by weight; vegetable oils; and hydrocarbons having aboiling point below 160° C., these feedstocks being cracked individuallyor as a mixture in the cracking zone of the process.

The solid carbon material in the fluidized state containing the cokedmaterial may be injected into the dense phase of at least one step ofthe regeneration zone when this is a multistage zone.

The Dispersion of solid carbon material in the fluidized state may beobtained by means for dispersing said material over the entire sectionof the regeneration zone so that the ratio of the distribution of thecatalyst particles to that of the carbon material within theregeneration zone is close to 1. In other words, the proportion ofcatalyst particles over carbon material particles is constant in anypoint of the section of the regeneration zone.

For this purpose, the regeneration zone may be equipped with at leastone structured packing, placed upstream and/or downstream of means fordispersing the carbon material relative to the envisaged circulation ofthe catalyst in said regenerator, whatever the dispersing means.Advantageously, this structured packing will be placed upstream from themeans for dispersing the carbon material.

The regeneration zone may be equipped with at least one structuredpacking for dispersing the coked catalyst particles and the homogeneousdispersion of solid carbon material in the fluidized state may becarried out countercurrently of the catalyst circulation, downstream ofsaid structured packing, said packing covering all or part of thesection of said regeneration zone.

For example, the homogeneous dispersion may be carried out in thepresence of at least one packing placed in the dense phase of a firststage of the regeneration zone in the case of a multistage regenerationzone.

The solid carbon material in the fluidized state may be dispersed overall or part of the height of each dense bed of the regeneration zone,each dispersion taking place after the fluidized bed has beenhomogenized, this bed being optionally equipped with at least onestructured packing.

The invention also relates to a plant for implementing the processaccording to the invention, comprising at least a main reactor andpossibly at least a secondary reactor, at least a disengager/stripper,and a single-stage or multistage regenerator, characterized in that itincludes means for homogeneously dispersing a carbon material in thedivided state over coked catalyst particles coming from thedisengager/stripper, these homogeneously dispersing means being locatedupstream of the regenerator and/or in the regenerator itself. Accordingto the invention, the regenerator is further equipped with at least onestructured packing, placed upstream and/or downstream of means fordispersing the carbon material relatively to the envisaged circulationof the catalyst within the regenerator.

The means for dispersing the carbon material may be placed in a lineconnecting the stripper to the regenerator and conveying the strippedcoked catalyst to said regenerator.

The means for dispersing the carbon material may also be placed in adense part of the fluidized bed in the regenerator.

Optionally, means for dispersing the carbon material may be placed atthe two locations described above.

When the dispersing means are placed in a line connecting the stripperto the regenerator and conveying the stripped coked catalyst to saidregenerator, they may comprise a hopper for storing carbon materialpreground to the desired particle size. It if for example possible touse the same hopper for storing and injecting both the catalyst, whetherfresh or equilibrium (issued from the cracking zone) catalyst, and thecarbon material particles.

When the dispersing means are placed in the regenerator, they may bechosen from means capable of dispersing gas/solid mixtures in a densebed. They are preferably open tubes and/or rakes formed from severalparallel tubes opening into the dense bed, these tubes being connectedto a manifold tube.

The regenerator may be equipped with at least one structured packing,placed upstream and/or downstream of the means for dispersing the carbonmaterial relative to the envisaged circulation of the catalyst in saidregenerator.

In particular, the regenerator may be equipped with at least onestructured packing, placed upstream of the means for dispersing thecarbon material relative to the envisaged circulation of the catalyst insaid regenerator within the dense fluidized bed of the firstregeneration stage.

These packings are for example formed by interlacing plates, strips orfins constituting a screen, this screen occupying less than 10% of thearea of the cross section of the vessel in which it is placed, covering,in projection on said section, the entire surface thereof.

DETAILED DESCRIPTION OF THE INVENTION

The feedstocks that an FCC unit according to the present invention cantreat are feedstocks having a Conradson carbon residue equal to or lessthan 0.1% by weight and having a hydrogen content equal to or greaterthan 12.7% by weight.

The present invention may be described as a process for the catalyticcracking of a weakly coking feedstock having a Conradson carbon residueequal to or less than 0.1% by weight and a hydrogen content equal to orgreater than 12.7% by weight, this process being implemented in a unitcomprising at least a feedstock cracking zone, a zone forseparating/stripping the effluents from the coked catalyst particles anda zone for regenerating said particles, the feature of the process beingthat at least a solid carbon material in the fluidized state, the carboncontent of which is equal to or greater than 80% by weight, is injectedupstream of and/or during the catalyst regeneration step, into a densefluidized bed of coked catalyst particles.

According to the invention, the process is such that:

-   -   (a) at least one solid carbon material in the fluidised state,        having a carbon content equal to or greater than 80% by weight,        is dispersed on the coked catalyst particles:        -   (i) upstream of the regenerating zone and downstream of the            separating/stripping zone, and/or        -   (ii) in the zone for regenerating catalyst within the coked            catalyst particles of a dense bed.    -   (b) the amount of solid carbon material in the fluidized state        dispersed within the coked catalyst particles of the dense bed        is adjusted so as to deliver an additional amount of coke Q_(C)        to the catalyst so as to satisfy the following equation (I):        Q _(c) =Q _(t) −Q _(i)  (I),        in which Q_(i) is the initial coke content of the coked catalyst        after the feedstock has been cracked and Q_(t) or delta coke is        the coke content necessary for maintaining the temperature of        the regenerated catalyst and therefore the heat balance of the        process,    -   (c) the mixture of coked catalyst particles and solid carbon        material is burnt in the regeneration zone to produce a        regenerated catalyst having a reduced content of carbon        material,    -   (d) the regenerated catalyst is mixed with the weakly coking        feedstock in the cracking zone to produce the coked catalyst        particles and the effluents,    -   (e) the coked catalyst particles are separated from the        effluents in the separating/stripping zone, then the coked        catalyst particles are sent back to the regeneration zone.

To divide, or even fluidize, the particles of solid carbon material in aliquid or gaseous effluent, any means similar to that used in particularfor fluidizing catalyst may be used, said effluent having to keep theparticles of said material divided and non-amalgamated. Preferably, airis used as effluent for fluidizing this solid carbon material in thedivided state.

The term “regeneration zone” is understood to mean a zone in which aregeneration of the coked catalyst is performed which takes place in oneor more steps, generally two steps, in one and the same vesselcomprising one or more stages and/or in different regeneration vesselscomprising one or more steps in one or more stages.

The cracking zone, dedicated to the cracking of the feedstock, comprisesat least one reactor, in particular at least one main reactor and atleast one secondary reactor.

The separating/stripping zone is dedicated to separating and strippingthe coked catalyst particles from the effluents issued from the crackingof the feedstock. This separating/stripping zone comprises at least onedisengager and at least one stripper.

A weakly coking feedstock is a feedstock that will produce a weaklycoked catalyst at the outlet of the cracking reactor, the amount of cokenot being high enough to maintain the heat balance of the catalyticcracking unit in which it is used, typically said amount is less than0.4% by weight. Specifically, the regeneration of the catalyst, byburning off the coke, releases heat that should be recovered insufficient amount by the catalyst so that the latter supplies, on theone hand, energy sufficient to vaporise almost completely the feedstockinjected in liquid form into the reactor and supplies, on the otherhand, sufficient energy to the generally endothermic cracking reactionsso as to maintain a reaction temperature at the outlet of said reactorwhich is generally between 480 and 650° C. depending on the desiredconversion objectives and configurations.

To enable said carbon material to be dispersed, the present inventionuses any means for homogeneously dispersing a solid material, such asthose currently used for injecting fresh catalyst into a dense catalystbed. For better compatibility between coked catalyst particles andparticles of the carbon material, measures will be taken to ensure thatthe particle size of the carbon material is best suited for making itpossible not only to obtain good fluidization behaviour but also tolimit elutriation of the particles of highly carbonaceous material inthe dilute phase above the dense bed. For this purpose, the particlesize of the added carbon material(s) may advantageously be roughlyidentical to the particle size of the catalyst particles. The term“roughly identical” means an identical size with a variation of ±10%.

The advantage of the present invention is essentially that the amount ofcoke in the regenerator is increased, thus making it possible tocompensate for the small amount of coke formed by the feedstock in thecracking reactor. This increase in the amount of coke to be burnt off inthe regenerator, having a very low hydrogen content, has the effect ofincreasing the heat resulting from the combustion of the coke andconsequently of increasing the temperature of the resulting regeneratedcatalyst particles that will be recycled into the main reactor in asingle-reactor configuration and to the main and secondary reactors in atwo-reactor configuration. The final advantage is to make it possiblefor the amount of coke needed for thermal equilibrium of the unit to beadjusted as required and thus to ensure that said unit operatesefficiently.

For efficient operation of the FCC unit fed with a weakly cokingfeedstock, the amount of coke (Q_(t)) present on the catalyst enteringthe regeneration zone, necessary for equilibrating the heat balance,will correspond to the sum of the initial amount of coke (Q_(i))supplied by the cracking of the feedstock on the catalyst (in the mainreactor or in the two or more reactors of the FCC unit) and of theamount of coke (Q_(c)) supplied by fluidizing the carbon material on thecoked catalyst after the feedstock has been cracked. In general, Q_(t),namely the amount of coke entering the regenerator, typical for abalanced heat balance, is maintained between 0.5 and 1% by weight whenthe combustion is in the case of a single-step regeneration zone andbetween 0.8 and 1.45% by weight for partial combustion in the first stepof a regeneration zone of a multistage regenerator comprising at leasttwo regeneration steps.

In the context of the present invention, the amount of carbon materialdispersed within the coked catalyst particles is adjusted so as todeliver an additional amount of coke Q_(C) to the catalyst so as tosatisfy the following equation (I):Q _(c) =Q _(t) −Q _(i)  (I),in which Q_(i) is the initial coke content of the coked catalyst afterthe feedstock has been cracked and Q_(t) or delta coke is the cokecontent necessary for maintaining the temperature of the regeneratedcatalyst and therefore the heat balance of the process.

To implement the invention, the carbon material having a carbon contentequal to or greater than 80% by weight may be chosen among:

-   -   coke having a hydrogen content equal to or less than 10% by        weight, this coke resulting from: the coking of coal; cokers for        hydrocarbon effluents having a boiling point above 350° C.        chosen from heavy effluent fractions coming from a cracking        reaction, HCOs (heavy cycle oils) with a distillation range        typically between 360 and 440° C. and slurries with a        distillation range above 360° C. (denoted by 360°+);    -   biomass residues coming from the conversion of wood and/or        cellulose;    -   powdered coal dissolved in a fluid hydrocarbon and/or injected        by blowing or spraying;    -   asphalt-rich fractions coming from deasphalting units;    -   non-utilizable waxes coming from the liquefaction of coal by an        indirect (GTL) process or from a Fischer-Tropsch process for        converting gas into hydrocarbons; or a mixture of said        fractions.

Among the weakly coking feedstocks that the present invention can treatmay be found the following:

-   -   purges from a hydrocracker unit, called bleeds, having a        hydrogen content equal to or greater than 12.7% by weight;    -   severely pretreated VGO (vacuum gas oil, resulting from the        vacuum distillation of atmospheric distillation residues)        feedstocks, generally having a boiling point above 350° C. and        having hydrogen contents equal to or greater than 12.7% by        weight;    -   vegetable oils; and    -   hydrocarbons having a distillation point of 160° C. or below,        such as gasolines, or even certain liquefied gas molecules such        as butane, coming from distillation and/or conversion units.

These feedstocks may be cracked individually or as a mixture in the mainreactor of the catalytic cracking unit.

The present invention involves the production of effluents such as, forexample, petrol (gasoline) and LPG (liquefied petroleum gas) from aweakly coking feedstock, such as one of those mentioned above, by fluidcatalytic cracking (FCC) in a corresponding unit that has at least onemain reactor operating in upflow mode (riser reactor) or in downflowmode (downer reactor), the coked catalyst leaving the reactor beinginjected into a separating/stripping zone at the outlet of which thecoked catalyst is recovered and sent into the regenerator of the unit.The regenerator may be a single-stage or multistage regenerator. In thecase of a single-stage reactor, this comprises at least one fluidizedbed of coked catalyst particles, in which the combustion of the coketakes place, these being distributed according to their respectiveaverage density, including at least one dense-phase bed in which most ofthe combustion takes place, and at least one dilute-phase bed in whichthe completely or partly decoked catalyst particles separate from thegaseous effluents resulting from the combustion. It is in that part ofthe dense fluidized bed in which the combustion reaction is the mostcomplete that the catalyst may reach the intended temperature before itis recycled to the main reactor. It is therefore into the dense bed thatthe carbon material is injected in fluidized form.

In order for the carbon material injected in fluidized form to behomogeneously blended within the catalyst particles, it is necessary todisperse the particles of carbon material over the entire cross sectionof the bed by suitable dispersing means so that the ratio of thedistribution of the catalyst particles to that of the particles ofcarbon material is close to 1. One of the means for achieving such aratio is to homogenise the dense phase of the fluidized bed by theinsertion of structured packings that improve the dispersion of thecoked catalyst particles upstream of the dispersing of the particles ofcarbon material, this dispersing operation being carried out by anymeans. The structured packings may cover all or part of the crosssection of the regenerator and over at least a portion of the heightthereof. Thus, it would be conceivable to inject, possibly in a stagedmanner, the carbon material over all or part of the height of the densebed, each dispersion of carbon material taking place after the fluidizedbed has been homogenised by means of a structured packing.

By using structured packings it is possible to provide a continuouscatalyst stream of homogeneous density. In a preferred embodiment, thesepackings occupy less than 10% of the area of the flow cross section inthe vessel in which they are placed, although in projection on saidvessel they occupy the entire area thereof.

One of the advantages associated with using such packings is that theymake it easier for homogenisation and combustion of the carbon materialinjected into the dense phase, thereby limiting the occurrence of hotspots in the fluidized bed. Another advantage is that the entrainment ofincompletely burnt carbonaceous particles into the gases output from theregenerator is limited.

When a multistage regenerator comprising at least two regenerationstages is operated, the first stage serves for the partial combustion ofthe coke present on the catalyst particles coming from the reactor, thispartial combustion leading to the formation of CO and most particularlysteam coming from the hydrogen atoms present. Since the combustion ispartial, even if there is steam formation close to the catalystparticles, the reaction temperature is lower and the probability ofreducing the activity of the catalyst particles is lower. The additionof carbon material having a hydrogen content of less than 10% by weightwill not disturb the partial combustion if the amount of carbon materialrelative to that of the coked catalyst particles is equivalent, that isto say with a mass ratio close to 1. As regards the second stage, thisbehaves as a single-stage regenerator in complete combustion mode.

In the context of the present invention, it is possible to inject carbonmaterial in the fluidized state both into the first regeneration stageand into the second regeneration stage, but always into the dense phaseof the fluidized bed contained in these stages. This injection could beimproved by inserting structured packings as described above, upstreamof the dispersing of the carbon material in said bed. Moreover, it ispreferable to inject carbon material into the first stage of theregenerator (the one having two regeneration stages) in order to havemore time to finalise the combustion of the carbon material particles.

However, the injection of coke coming in particular from cokers posesother problems in the operation of the unit. Coke such as coke from acoker, also called “petcoke”, generally contains many heavy metals suchas nickel and vanadium that are poisons for the catalytic activity ofthe catalyst used in FCC units, but also contains sulphur and nitrogen,the amount of which must be limited. It is known that the amount ofheavy metals that can be tolerated in the catalyst of an FCC unit is atmost 10 000 ppm, preferably less than 6500 ppm for a two-stageregenerator and from 5000 to 7000 ppm for a single-stage regenerator. Tocontrol the amount of heavy metals accumulated in the catalyst, acomplement of fresh or equilibrium catalyst, called “flush cat” by thoseskilled in the art, is injected into the regenerator so as to reduce theamount of metals circulating in the unit. The presence of nitrogen andsulphur in the coke injected into the regenerator will inevitably leadto the formation of undesirable polluting species in the flue gasleaving the regenerator, such as NOx and SOx. To limit the formation ofthese species during combustion of the coke, commercial additives,called “DeSOx” additives, known to those skilled in the art may be used.These additives, sold by all catalyst vendors, help to capture the SO₂in the regenerator and transport it to the reaction zone where, in thepresence of steam, the SO₂ is then released in the form of sulphurousacid (H₂SO₃), which will then be recovered in the cracked-gas scrubbingsection. In the case of NOx, the preferred solution is of the SCR(selective catalytic reduction) or SNCR (selective non-catalyticreduction) type. Finally, mention should be made of flue gas scrubbersthat can abate both NOx and SOx, and also catalyst particles. In allcases, it is necessary to carry out a technico-economic study so as toselect the most appropriate flue gas treatment option in accordance withthe discharge legislation.

Another subject of the present invention is a plant for implementing theinvention, comprising the various vessels needed to implement acatalytic cracking process, that is to say at least a main reactor andpossibly at least a secondary reactor, at least a disengager and astripper and a single-stage or multistage regenerator, said plantincluding means for homogeneously dispersing a carbon material in thedivided state on the coked catalyst particles upstream of theregenerator and/or in the regenerator itself. These homogeneousdispersing means are for example those used for injecting fresh catalystinto a dense catalyst bed.

These dispersing means may comprise a hopper for storing carbon materialpreground to the desired particle size. The carbon material particlesare preferably maintained in the fluidized state by injecting air intothe hopper. In the hopper an injection system serves to transport thecarbon material particles to the regenerator using a carrier gas,typically air, the flow rate of which is adjusted by a restrictingorifice, and enabling the amount of carbon material sent to the densephase of the regenerator to be controlled. The system here is similar tothat used for injecting fresh catalyst into any FCC unit, as known tothose skilled in the art. It should be mentioned that, in many possiblevariants of the invention, it is possible to use the same hopper forstoring and injecting both the catalyst, whether fresh or equilibriumcatalyst, and the carbon material particles.

The dispersing means, when they are placed in the regenerator, may alsobe chosen among means capable of dispersing gas/solid mixtures in adense bed. They are preferably open tubes and/or rakes formed fromseveral parallel tubes opening into the dense bed, these tubes beingconnected to a manifold tube.

According to the invention, the regenerator is further equipped with atleast one structured packing, placed upstream and/or downstream of themeans for dispersing the carbon material relatively to the envisagedcirculation of catalyst within the regenerator.

In a first embodiment of the plant, the carbon material dispersing meansare placed in a line connecting the stripper to the regenerator andconveying the stripped coked catalyst to said regenerator.Advantageously, at least one structured packing may be placed in saidline between the stripper and the regenerator, after the point ofinjection of the carbon material particles (relative to the envisagedcirculation of catalyst in said regenerator), in order to ensure betterhomogenisation of the carbon material/catalyst blend.

In a second embodiment of the plant, the dispersing means areadvantageously placed in part of the dense bed. The regenerator will beequipped with at least one structured packing, placed downstream and/orupstream of the carbon-material dispersing means with respect to theenvisaged circulation of catalyst in said regenerator.

In a variant, several packings, each being associated with acarbon-material dispersing means, may come one after another with atleast one packing associated with a dispersing means.

As packing elements, one or more of the structured packings described inthe patents EP 719 850, U.S. Pat. Nos. 7,022,221, 7,077,997, WO2007/094771, WO 00/35575 and CN 1 763 150 may be used. Here, in each ofthe envisaged packings, the stream of coked particles is aerated bymaking them follow preferential pathways obtained by interlacing plates,strips or fins constituting a screen. The cross section of this screenparallel to the cross section of the vessel containing it may occupyless than 10% of the area of the flow cross section of said vessel but,in projection on said section, it may cover the entire area thereof.Such interlacing is generally arranged in layers of the same type,enabling this aerating of the particles to be controlled.

Upstream of the dispersing means of the carbon material, the raw carbonmaterial is finely ground and then screened, and only the particleshaving the required size, i.e. approximately the size of the freshcatalyst particles, are sent into a line into which a carrier gas,typically air, is injected, thereby entraining the divided solid intothe devices for dispersing it in the coked catalyst.

The dimensioning of such a dispersing device follows the same designrules as those used by a person skilled in the art for pneumaticallytransporting a finely divided solid, such as the catalyst, from itsstorage hopper to its point of injection into a dense bed. Among themeans capable of dispersing the gas/solid mixtures in a dense bed, it ispreferable to use open tubes and/or rakes formed from several paralleltubes opening into the dense bed, these tubes being connected to amanifold tube.

Whatever the device for dispersing the carbon material in the dense bed,the regenerator may be operated in total or partial combustion mode, inpresence of a gas containing oxygen. For operation in partial combustionmode, the injected air is not able to burn off all of the coke presentin the regenerator, coming from both the coke on the coked catalystparticles and from the carbon material particles intentionally injectedinto the regenerator. In this case, coke particles will move towards thereaction zone. The advantage of such a situation is the ability todilute the catalytic activity of the circulating catalyst mass andtherefore to reduce the degree of conversion of the treated feedstock soas to maximise the production of distillate. Another advantage of thisoperation in partial combustion mode is that the heat balance is notsignificantly modified since the coke particles are at the temperatureof the dense phase in the regenerator.

The invention will now be described with reference to the appendednon-limiting drawings in which:

The FIGURE is a section through a regenerator equipped with a system fordispersing carbon material particles in a gaseous fluid up to the inletof the dispersion device therein: two arrangements are possible, namelyAB and BC, depending on whether the carbon material is injected into theline between the stripper and the regenerator or directly into theregenerator (for example via another line).

The FIGURE shows, in its main part B, a regenerator (1) containing adense catalyst bed (2) equipped with two cyclones (3) for a finalgas/solid separation before the CO₂-laden combustion gas is discharged.The regenerator (1) is equipped with an inlet (4) for the cokedcatalyst, with a line (5) for discharging the regenerated catalyst and,at the bottom, an air inlet. The regenerator (1) is coupled with acarbon material, for example coke, injection system in two possibleconfigurations, AB and BC. These two systems for injecting the carbonmaterial corresponding to the parts A and C are shown in the FIGURE. Ineach part A or C, the carbon material is ground in vessels (6 or 6′) andthen the carbon material, in the form of powder particles, is sent intoa line (4) in the AB configuration or a line (8) in the BCconfiguration. In the latter configuration, the line (8) is equippedwith an air blower (7) capable of keeping the injected carbon materialparticles in the fluidized state circulating up to the regenerator wherethe carbon material is blended with the dense bed of coked catalyst. Thelines (4) and (8) are equipped with injectors (9) and (9′) for injectingDeSox and DeNOx additives.

Examples are given below to illustrate the invention, but they shouldnot be interpreted as limiting the invention.

EXAMPLE

This example shows the advantages of the present invention by comparingthe efficiency in terms of product yield when weakly coking feedstocksare cracked in an FCC unit with and without recycle of coking fractions.

The production of coke in the coker was 250 t/h of the followingcomposition: C=85.2 wt %; H=3.6 wt %; N=1 wt %; S=7.5 wt %; Ni=179 ppm(by weight); and V=565 ppm (by weight). The calorific value of the cokewas assumed to be equal to 7.75 kcal/kg. This coke is the coked used inthis example.

A base case may be distinguished in which there is no coke injectionusing an FCC unit having a single riser reactor with a capacity of 4800tonnes per day, i.e. 200 tonnes per hour, and treating a correspondinghydrotreated VGO feedstock, the properties of which are given below.

TABLE 1 Properties of the hydrotreated VGO Feedstock Hydrotreated VGODensity g/cm³ 0.8610 H₂ content wt % 13.7 Sulphur content ppm by weight330 Nitrogen content ppm by weight 550 CCR (Conradson carbon residue) wt% <0.1 Ni content ppm by weight <2 V content ppm by weight <2

Trials on a pilot plant have shown that this feedstock produced verylittle coke, about 3.3% for a reaction temperature of 525° C. and a C/Oratio of 8. On the basis of this pilot data, we carried out heat balancecalculations under various operating cases of an industrial unit which,by definition, must close the heat balance thereof. The results of thesecalculations are given in Table 2 below. The heat balance calculationswere carried out on the basis of the calculation formulae mentioned inthe work: “Fluid Catalytic Cracking Handbook”, second edition (2000) byReza Sadeghbeigi, published by Gulf Professional Publishing.

TABLE 2 Case 1 Case 2 Case 3 Feedstock throughput t/h 200.0 200.0 200.0Ni eq. ppm 0.1 4.0 2.9 V eq. ppm 0.1 12.7 9.1 Rate of fresh catalystaddition t/day 2.00 10.60 8.20 Active surface area of the catalyst m²/g147.3 146.5 146.9 Ni content on the catalyst ppm 120 1811 1698 V contenton the catalyst ppm 120 5660 5327 Reaction temperature (RT) ° C. 525.0525.0 525.0 Catalyst flow rate t/min 26.8 24.3 24.4 C/O ratio — 8.037.29 7.32 % coke (delta coke) on the catalyst wt % 0.41 0.45 0.45Feedstock preheat temperature ° C. 416.4 208.2 273.7 Preheat furnaceinlet/outlet temperature difference ° C. 208.2 0.0 65.5 Energy deliveredby the feedstock preheat furnace Mkcal/h 32.4 0.0 9.3 Dense phasetemperature (= T_(regen)) ° C. 627.2 714.4 691.6 Energy to be deliveredto the Mkcal/h 0 35 25 regenerator Standard Conversion wt % 83.8 83.983.7 H₂S wt % 0.01 0.01 0.01 H₂ wt % 0.00 0.01 0.01 C1-C2 wt % 1.40 1.451.45 C3-C4 wt % 23.4 23.4 23.3 Standard LCN C5-160 wt % 44.1 44.1 44.0Standard HCN 160-220 wt % 11.7 11.7 11.7 Standard LCO 220-360 wt % 11.511.5 11.6 Standard slurry 360₊ wt % 4.7 4.7 4.7 Coke wt % 3.3 3.3 3.3Total wt % 100.0 100.0 100.0 Rate of coke injection into the kg/h 0 45023215 regenerator Equivalent coke yield wt % 3.3 5.5 4.9 Throughput ofair injected into the t/h 91 152 135 regenerator

Table 2 shows three cases for the operation of an industrial unit.

In the first column entitled “Case 1”, or basic case without cokeinjection, no coke was injected into the regenerator and the preheattemperature of the feedstock injected into the reactor necessary forobtaining 3.3 wt % of coke with a reaction temperature of 525° C. wascalculated. In this case, to obtain heat balance of the unit, thefeedstock preheat temperature had to be very high and moreoverunacceptably high, since above 400° C. the feedstock starts to crackeven before it enters the reactor of the unit. In addition, thetemperature of the dense phase in the regenerator was barely 627° C.,again an unacceptable temperature as it was below the temperature atwhich the coke deposited on the catalyst contained in the regeneratorstarted to be burnt off.

Two other cases were envisaged for achieving both acceptable preheattemperatures for the feedstock injected into the reactor and acceptabletemperatures of the coked catalyst in the dense phase in theregenerator, with an industrial FCC unit operating with a balanced heatbalance.

In the configuration of case 2 in Table 2, coke was injected into theregenerator without the ancillary feedstock preheat furnace, thefeedstock being preheated only by a series of feedstock/effluent heatexchangers. In this case, the preheat temperature did not exceed 280° C.Therefore, to obtain a sufficiently high temperature of the cokedcatalyst in the dense phase of the regenerator, typically above 650° C.,and to achieve equilibrated heat balance in the unit, it was necessaryto supply energy by the combustion of additional coke. In this case, asupply of 35 Mkcal/h to the regenerator then made it possible to obtaina dense phase temperature of 714° C. For such a heat supply, it was thennecessary to inject about 4500 kg/h of coke from a coker into the cokedcatalyst to be regenerated.

The drawback of injecting coke from a coker into the regenerator is theintroduction of metals such as Ni and V, known to poison the catalyst,having the effect of deactivating the catalyst. Knowing the rate ofinjection of coke from a coker into the regenerator and the Ni and Vcontents, it was then possible to calculate the equivalent Ni and Vcontents relative to the feedstock deposited on the recirculatingcatalyst. This exercise allows us to calculate the catalyst make-upnecessary for maintaining a satisfactory level of catalytic activity inthe cracking unit. To be able to be compared with case 1, the catalystmake-up is adjusted so as to obtain the same level of active area, i.e.about 147 m²/g. Consequently, in comparison with the base case, it maybe seen that it was necessary to increase the catalyst make-up from 2t/day to 10.6 t/day, representing not insignificant additional operatingcost of the invention.

To limit this additional operating cost due to the injection of a highercatalyst make-up, the energy delivered to the regenerator by injectingcoke from a coker could be reduced by increasing that delivered by thefeedstock to the reactor. This is case 3, which consisted in injectingcoke into the regenerator while preheating the feedstock with a preheatfurnace on the feedstock feed line upstream of the cracking reactor.When the energy delivered to the regenerator was 25 Mkcal/h comparedwith 35 Mkcal/h, the amount of coke from a coker, to be injected intothe regenerator, could be reduced down to 3200 kg/h. By carrying out thesame exercise as previously, the fresh catalyst make-up was then reducedto 8.2 t/day, as opposed to 10.6 t/day. When the energy to theregenerator was reduced in this way for a coke yield produced by theequivalent feedstock, to achieve an acceptable heat balance of the unit,it was then necessary to supply energy to the catalyst in the crackingreactor by further preheating the feedstock. In this case, the preheattemperature had to be about 274° C. If the maximum preheat temperatureof the feedstock leaving the feedstock/effluent heat exchanger was 208°C., a furnace had to be added, after the heat exchangers, to the feedline for the feedstock to be cracked so as to raise the temperature ofthe feedstock from 208° C. to 274° C., thereby requiring 9.3 Mkcal/h ofheat supplied to the feedstock. In this case, the calculation of theheat balance showed that thermal equilibrium of the unit was thusachieved since the approximately 10 Mkcal/h reduction in energy suppliedby adding coke to the regenerator was compensated for by the supply ofenergy via the preheating of the feedstock using a furnace.

The operating cost savings associated with the reduction in catalystmake-up are therefore offset by the increase in operating costs due tothe use of heating fuel in the furnace for heating the feedstock. Froman economic standpoint, case 3 is not necessarily better than case 2.Indeed, the sum of the investment costs associated with the installationof a furnace, and for the consumption of a fuel of better quality burntin said additional furnace, is at least equal if not greater than thecost of the addition of ground coke from a coker, as described in case 2with an increased fresh catalyst make-up.

In case 3, the temperature in the regenerator was barely above 690° C.:it will be difficult to reduce the volume of coke injected into theregenerator further, and therefore the energy delivered thereby, withoutrunning the risk of compromising the efficient operation of theregenerator, i.e. complete combustion of the coke present on thecatalyst to be regenerated.

It should also be noted that the yields of cracking products remainequivalent in the three cases envisaged, except for a slight increase inthe volume of dry gases for cases 2 and 3 with coke injection, thisincrease being due to the presence of metals on the catalyst.

Finally, by calculating the equivalent coke yield relative to thefeedstock, it is possible to estimate the necessary air throughput intothe regenerator for simultaneous combustion of the coke deposited on thecatalyst, after cracking of the feedstock in the reactor, and of thecoke from a coker added to the regenerator, and to do so for the sameexcess flue-gas oxygen level.

The invention claimed is:
 1. A process for the catalytic cracking of aweakly coking feedstock having a Conradson carbon residue equal to orless than 0.1% by weight and a hydrogen content equal to or greater than12.7% by weight, implemented in a unit comprising at least a feedstockcracking zone, a separating/stripping zone for separating/strippingeffluents from coked catalyst particles and a regeneration zone forregenerating said coked catalyst particles, characterized in that: (a)at least a solid carbon material in a fluidized state, having a carboncontent equal to or greater than 80% by weight, is dispersed andinjected into a dense phase of a fluidized bed of the coked catalystparticles within at least one step of a regeneration zone forregenerating catalyst within the coked catalyst particles, wherein theregeneration zone comprises one or more structured packings fordispersing the coked catalyst particles, wherein a homogeneousdispersion of the solid carbon material in the fluidized state iscarried out countercurrently of catalyst circulation, downstream of theone or more structured packings, wherein each of the one or morestructured packings is formed by interlacing plates, strips or finsconstituting a screen, and wherein the one or more structured packingsoccupy less than 10% of the flow cross section area of the regenerationzone, (b) an amount of the solid carbon material in the fluidized statedispersed within the coked catalyst particles of the fluidized bed isadjusted so as to deliver an additional amount of coke Qc to the cokedcatalyst so as to satisfy the following equation (I):Qc=Qt−Qi  (I), in which Qi is an initial coke content of the cokedcatalyst particles after the feedstock has been cracked and Qt or deltacoke is a coke content necessary for maintaining a temperature ofregenerated catalyst and therefore a heat balance of the process, (c) amixture of coke on the coked catalyst particles and all of the dispersedand injected solid carbon material is burnt in the regeneration zone toproduce the regenerated catalyst having a reduced content of carbonmaterial, (d) the regenerated catalyst is mixed with the weakly cokingfeedstock in the feedstock cracking zone to produce the coked catalystparticles and the effluents, and (e) the coked catalyst particles areseparated from the effluents in the separating/stripping zone, then thecoked catalyst particles are sent back to the regeneration zone.
 2. Theprocess according to claim 1, characterized in that the solid carbonmaterial is fluidized in a liquid or gaseous effluent not amalgamatingwith other solid carbon material in the regeneration zone.
 3. Theprocess according to one of claim 1, characterized in that Qt is from0.5 to 1% by weight when the regeneration zone comprises only a singlestep and from 0.8 to 1.45% by weight for a partial combustion in a firststage of the regeneration zone of a multistage regenerator having atleast two regeneration steps.
 4. The process according to claim 1,characterized in that the solid carbon material is: coke resulting fromcoking of coal; coke from cokers for hydrocarbon effluents having aboiling point above 350° C. chosen from heavy effluent fractions comingfrom a main cracking reaction, heavy cycle oils with a distillationrange typically between 360 and 440° C., and slurries with adistillation range above 360° C.; biomass residues coming fromconversion of wood and/or cellulose; powdered coal dissolved in a fluidhydrocarbon and/or injected by blowing or spraying; asphalt-richfractions coming from deasphalting units; non-utilizable waxes comingfrom liquefaction of coal by an indirect gas-to-liquid (GTL) process orfrom a Fischer-Tropsch process for converting gas into hydrocarbons; orcombinations thereof.
 5. The process according to claim 1, characterizedin that the weakly coking feedstock injected into the feedstock crackingzone comprises one or more of the following feedstocks: purges or bleedsfrom a hydrocracking unit; feedstocks based on vacuum-distilled gas-oilfractions having a boiling point above 350° C. and having hydrogencontents equal to or greater than 12.7% by weight; vegetable oils; andhydrocarbons having a boiling point below 160° C., wherein thesefeedstocks are cracked individually or as a mixture in the feedstockcracking zone.
 6. The process according to claim 1, characterized inthat the dispersion of the solid carbon material in the fluidized stateis obtained by means for dispersing said solid carbon material over anentire section of the regeneration zone so that a proportion of catalystparticles over solid carbon material particles is constant in any pointof the regeneration zone.
 7. The process according to claim 1,characterized in that the dispersion is carried out in the presence ofat least one packing placed in a dense phase of a first step of theregeneration zone.
 8. The process according to claim 1, characterized inthat the solid carbon material in the fluidized state is dispersed overall or part of a height of each dense fluidized bed of the regenerationzone, each dispersion taking place after the dense fluidized bed hasbeen homogenized, wherein the dense fluidized bed is optionally equippedwith at least one structured packing.
 9. A process for the catalyticcracking of a weakly coking feedstock having a Conradson carbon residueless than or equal to 0.1% by weight and a hydrogen content greater thanor equal to 12.7% by weight, the process comprising: (a) catalyticallycracking a mixture comprising a regenerated catalyst and the weaklycoking feedstock to produce a coked catalyst; and (b) producing adispersion of a solid carbon material and injecting the dispersed solidcarbon material into a fluidized bed of the coked catalyst, wherein thefluidized bed of the coked catalyst is within a regeneration zone forregenerating the coked catalyst to provide the regenerated catalyst,wherein the solid carbon material has a carbon content greater than orequal to 80% by weight, and wherein the dispersed solid carbon materialis injected into a dense phase of the fluidized bed countercurrently ofcatalyst circulation; and (c) burning a mixture of coke on the cokedcatalyst particles and all of the dispersed and injected solid carbonmaterial in the regeneration zone to produce the regenerated catalystprior to recycling the regenerated catalyst to the step (a).
 10. Theprocess of claim 9, wherein the regeneration zone further comprises oneor more structured packings for dispersing the coked catalyst particles,and wherein each of the one or more structured packings comprisesinterlacing plates, strips or fins constituting a screen.
 11. Theprocess of claim 10, wherein the one or more structured packings occupyless than 10% of a flow cross section area of the regeneration zone. 12.The process of claim 11 further comprising injecting the dispersed solidcarbon material into the fluidized bed of the coked catalyst downstreamof the one or more structured packings.
 13. The process of claim 9further comprising: (d) adjusting an amount of the solid carbon materialinjected into the dense phase of the fluidized bed so as to deliver anadditional amount of coke Qc so as to satisfy the following equation(I):Qc=Qt−Qi  (I), in which Qi is an initial coke content of the cokedcatalyst particles produced in the step (a) and Qt is a coke content formaintaining a temperature of the regenerated catalyst.
 14. The processof claim 1, wherein the dispersed solid carbon material is injected intothe dense phase of the fluidized bed separately from introduction of thecoked catalyst thereto.
 15. The process of claim 14, wherein thedispersed solid carbon material is injected into the dense phase of thefluidized bed countercurrently from introduction of the coked catalystthereto.